Remove unneeded and buggy stats check

As per nodejs/node#39372 (comment)

Resolves #918

Author: RyanZim

lib/copy/copy-sync.js

@@ -154,7 +154,7 @@ function onLink (destStat, src, dest, opts) {
     // prevent copy if src is a subdir of dest since unlinking
     // dest in this case would result in removing src contents
     // and therefore a broken symlink would be created.
-    if (fs.statSync(dest).isDirectory() && stat.isSrcSubdir(resolvedDest, resolvedSrc)) {
+    if (stat.isSrcSubdir(resolvedDest, resolvedSrc)) {
       throw new Error(`Cannot overwrite '${resolvedDest}' with '${resolvedSrc}'.`)
     }
     return copyLink(resolvedSrc, dest)

lib/copy/copy.js

@@ -216,7 +216,7 @@ function onLink (destStat, src, dest, opts, cb) {
         // do not copy if src is a subdir of dest since unlinking
         // dest in this case would result in removing src contents
         // and therefore a broken symlink would be created.
-        if (destStat.isDirectory() && stat.isSrcSubdir(resolvedDest, resolvedSrc)) {
+        if (stat.isSrcSubdir(resolvedDest, resolvedSrc)) {
           return cb(new Error(`Cannot overwrite '${resolvedDest}' with '${resolvedSrc}'.`))
         }
         return copyLink(resolvedSrc, dest, cb)